OrcaFlex - Engineering Department

OrcaFlex
(latest release v9.3, Aug-09)
Wave energy and wave energy flux
• In a sea state, the average energy density per unit area of gravity waves on the
water surface is proportional to the wave height squared, according to linear
wave theory:
–
• where E is the mean wave energy density per unit horizontal area (J/m 2 ), the
sum of kinetic and potential energy density per unit horizontal area. PE=KE both
contributing half to the wave energy density E, as can be expected from the
equipartition theorem.
• As the waves propagate, their energy is transported. The energy transport
velocity is the group velocity. As a result, the wave energy flux, through a
vertical plane of unit width perpendicular to the wave propagation direction, is
equal to:-
• with cg the group velocity (m/s). Due to the dispersion relation for water waves
under the action of gravity, the group velocity depends on the wavelength λ, or
equivalently, on the wave period T. Further, the dispersion relation is a function
of the water depth h. As a result, the group velocity behaves differently in the
limits of deep and shallow water, and at intermediate depths.
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